Fuse Saver

This circuit will be particularly useful to those hobbyists who use a ‘breadboard’ to try out ideas and who also use a simple ‘home-made’ DC power supply consisting of a transformer, rectifier, smoothing capacitor and protective fuse, that is, one without over current protection! In this circuit, the detecting element is resistor R6. Under normal conditions, its voltage drop is not high enough to switch on transistor T1. The value of R6 can be altered to give a different cut-off current, as determined by Ohm’s Law, if required. When a short circuit occurs in the load, the voltage rises rapidly and T1 starts to conduct. 

This draws in the relay, switching its contacts, which cuts off power to the external circuit, and instead powers the relay coil directly, latching it in this second state. The circuit remains in this state until the primary power supply is switched off. Capacitors C1 and C2 hold enough charge (via D3, D4 and D6, which prevent the charge from being lost to the rest of the circuit, whichever state it is in) to keep T1 switched on and power the relay while it switches over, and R2 and R4 provide slow discharge paths. LEDs D1 (red) and D5 (green) indicate what state the circuit is in. Inductor L1 slows the inrush of current when the circuit is switched on, which would otherwise cut off the circuit immediately.

Circuit diagram:

Fuse Saver Circuit Diagram

D2 and D7 provide the usual back-emf protection across the coils. In use, the input of the circuit is connected to the main transformer-rectifier-capacitor-fuse power supply via K1, and the output is connected to the (experimental) load via K2. Note that the input voltage must be a floating supply if Vout– is grounded via the load, as Vin– and Vout– must not be connected together. Some consideration needs to be given to a number of components. First, the choice of relay Re1. For the prototype, this was obtained from Maplin, part number YX97F. This is has a coil resistance of 320 ?, which with R1 forms the collector load for T1. 

Its allowed pull-in voltage range is nominally 9 V to 19 V, which limits the input power supply voltage to between around 10 V to 30 V (DC only). R1 could be replaced by a wire link for operation at input voltages below 10 V, or increased in value, as determined by either the application of Ohm’s Law once more or trial and error, for an input voltage above 30 V. Coil L1 was obtained from Farnell, part number 581-240. Finally, the protective fuse for the input power supply should be a ‘slow-blow’ type; ‘fast’ fuses will rupture before the relay has time to switch. Also note that this device is meant to save fuses, not replace them. A mains transformer must always be fused if it is not designed to run safely, i.e., without presenting a fire hazard, even if its output has a continuous short-circuit fault.

 

 

Streampowers

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PC Power Saver

This circuit is designed to help minimise the  quiescent power consumption of PCs and  notebooks, the usage of simply our previous buddy the 555  timer and a relay as the major parts. The  circuit itself dissipates round zero.5 W in operation (that is, when the linked PC is on);  when switched off (with the relay not energised) the entire power draw is precisely zero. A prerequisite for the circuit is a PC or note e-book with a USB or PS/2 keyboard socket that  is energyed best when the PC is on. The power saver can be used to change PCs  and even whole multi-way extension leads. The unit can additionally be constructed  into  an  ordinary  mains  adaptor (which will must have an earth  pin!) because the photograph of the  creator‘s prototype shows. The  PC is plugged in to the socket  at the output of the ability saver  unit, and an extra connection  is made to the keep watch over enter of  the unit from a PS/2 (keyboard or mouse) socket or USB port. Only  the 5 V provide line of the interface is used.

 

  

PC Power Saver Image

When button S1 on the facility saver  is pressed the unit turns on, and the  monostable shaped by using the 555 timer is  brought about by means of the network composed with the aid of  R4 and C7. This drives relay RE1, whose contacts close. The connected PC isn't anyw tentatively powered up by means of the relay for a length  determined  by  P1  (approximately in the vary from 5 s to 10 s). If, all through this interval, the PC fails to indicate  that it is alive through supplying 5 V from its USB or  PS/2 connector (that is, if you don't change  it on), the monostable duration will expire, the  relay will drop out and any related device  will be energyed down. No further current will  be drawn from the provision, and, after all, it  might not be that that you may imagine to turn the PC on. When-ever you want to have to show the PC on, you must  always press the button on the ability saver  quickly earlier thanhand. 

If, however, 5 V is delivered through the PC to the  input of optocoupler IC2 earlier than the monostable occasions out (which will be the case if the  PC is changeed on all over that length), the  transistor within the optocoupler will conduct  and discharge capacitor C6. The monostable  will now stay prompted and the relay will  stay energised except the PC is changeed off  and power disappears from its USB or PS/2  interface. Then, after the monostable time  duration expires, the relay will drop out and the  power saver will disconnect itself from the primarys. There isn't any want to switch anything  else off: just shut down the gadget and the  power saver will deal with the stayder.

 

Circuit diagram :

PC Power Saver Circuit Diagram

 

It is additionally  imaginable to leave the computing device as it replaces its  tool, and the ability saver will do its job  quickly after the laptop shuts down. Power for the unit itself is obtained using a  simple provide circuit based around a miniature transformer. Alternatively, a 12 V mains  adaptor can be utilized, so lengthy as a relay with a  12 V coil voltage is used for RE1. In hellos proto-type the author used a relay with a 24 V coil  connected as proven immediately to the positive  facet of reservoir capacitor C2, the 555 being  energyed from 12 V regulated from that sup-ply using R1 and D1. A fixed resistor can of  path be used instead of P1 if desired. If the  adjustment vary of P1 isn't adequate (for  example if the PC energys up very slowly) the  monostable period may additionally be elevated via the usage of  a larger capacitor at C6.  The relay must have at the least two normally-open (or changeover) contacts rated at at  least eight A. The contact in parallel with S1 is used to provide energy to the device  itself, and the opposite contact carries  all of the current for the linked  PC  or  for  the  ex tension  lead  to  which  the  PC  and  peripherals  are  related. 

Pushbutton S1 must be rated for 230 VAC  (US: one hundred twenty VAC) operation: this is no place to  make economies. The coil current for the relay  floats thru LED D5, which must therefore  be a 20 mA sort. If a low-current LED is used,  a one hundred twenty Ω resistor may additionally be connected in parallel with it to carry the staying current.  The Fujitsu FTR-F1CL024R relay used in the  creator’s prototype has a rated coil present of  16.7 mA. Optocoupler IC2 offers isolation between  the circuit and the PC, and that is protected from  reverse polarity connection with the support of diode D4. The power saver must be constructed into an insulated enclosure and great care should be  taken to be certain that there is right kind isolation  between parts and wires carrying the  majors voltage and the other phases of the circuit. In phaseicular, the connection to the PC  and related elements (R6, C5, D4 and  IC2) must be in moderation arranged with as a minimum  a 6 mm hole between them and any section of  the circuit at majors potential.

 

Author : Wolfgang Gscheidle (Germany) - Copyright : Elektor

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